Mobile phone and wireless communication use is continuously expanding. Often mobile phones are used in noisy real life environments and/or in a hands free operation mode which results in degradation of the mobile telephone speech because of the noise found in real life environments. Speech enhancement of audio signals can be applied to improve the quality and intelligibility of speech degraded by noise. An approach to speech enhancement is post processing, where the output of a speech decoded signal is further processed. One example of this is the post-processing block in the adaptive multi-rate (AMR) narrowband codec standard (operating within the 0.3 to 3.4 kilohertz frequency range).
Post-processing can further be used to overcome quantisation noise generated by low bit rate speech encoders. Post-processing can be typically implemented in the form of post-filtering. In other words filtering the decoded speech signal with an adaptive filter in order to reduce the effects of environmental noise and enhancing the perceptual quality of the speech.